Acoustic panel



April 1959 H. SUSSMAN 2,884,084

ACOUSTIC PANEL Filed Oct. 28, 1954 IN VEN TOR. flflkl? 7 5055/1119 BY Q flrrok ers nite Sta es a -fi 2,884,084 ACOUSTIC PANEL Harry Sussman, Waterford, Conn., assignor to the United States of America as represented by the Secretary of the Navy Application October 28, 1954, Serial No. 465,452 5'Claims. (Cl. Isl-a5) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention concerns an acoustic panel and in particular concerns an acoustic panel capable of reflecting sound in water or other fluids.

There exists a need for acustic panels of this type in connection with underwater sound test targets, underwater acoustical shields and Wherever a sound reflector is required for use in water or other fluids. It is known that sound reflections will take place from objects in fluids if their specific acoustic impedance which is the product of density and the sound velocity differs from that of the fluid. It is also known that a highly compliant material such as cellular rubber is an excellent underwater sound reflector and has found many applications. However, under continued exposure underwater the enclosed gas in the cellular rubber gradually diffuses out with a resultant loss of the effectiveness as a sound reflector.

In contrast with the prior art method of using cellular rubber directly exposed to water, I have found that loss of gas from the cellular rubber can be prevented by enclosing the cellular rubber sheet in a rigid metal envelope with all edges sealed against Water entry. Although this is a new discovery, I have found it to have the disadvantage of being expensive and very diflicult to apply to objects of complicated shapes. Furthermore, exposure of such metal enclosed cellular structures in great depths can possibly cause them to warp and fail. To overcome the defects of using cellular rubber directly exposed to the water whereby enclosed gas gradually diffuses out and to overcome the disadvantages of my own discovery of enclosing the cellular rubber sheet in a rigid metal envelope with all edges sealed against water entry, I have discovered that protection against diffusion of gas through the rubber cells is provided by a compliant impermeable envelope placed around the cellular rubber or molded to it and this structure is, in turn, protected by a compliant layer of rubber or plastic. In my preferred form, several of these pieces are joined together in spaced relation to form a compartmented panel. The resulting structure is highly compliant and can withstand high hydrostatic pressures, there are no metal parts exposed to water to present corrosion problems, the panel can be wrapped around complicated shapes, and compartmentation prevents failure of the entire structure in case of a puncture or leak.

An object of the invention is to provide an acoustic panel.

Another object is to provide an acoustic panel capable of reflecting sound in water or in other fluids.

Another object is to provide an acoustic panel in which the entire structure is highly compliant and can withstand high hydrostatic pressures.

Another object is to prOYiQe an acoutsic panel that is free of metal parts exposed to water thereby avoiding corrosion problems.

Another object is to provide an acoustic panel that may be wrapped around complicated shapes.

Another object is to provide an acoustic panel having compartmentation that prevents failure of the entire strue ture in case of a puncture or leak.

Other objects and many of the attendant advantages of this invention-will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

The single figure is an isometric view of a preferred embodiment of the invention.

In the drawing there is shown multiple core pieces of cellular rubber or compliant cellular plastic 11 that are of rectangular shape. Each core piece 11 is enclosed in an individual gas-impermeable envelope 12 that can be made of thin metal foil, cellophane, polyvinyl alcohol or like materials. Each gas impermeable envelope 12 is sealed by suitable means such as heat or if desired, glue can be used. Core pieces 11 are arranged in spaced relation upon a sheet 13 of rubber. Strips of unvulcanized rubber 14 are placed in the spaces between core pieces 11 and along the outer borders. A covering sheet of rubber 16, is placed over the assembly. The assembly is then vulcanized by means of 'heat and pressure to form watertight seals 15 around each core piece 11 of cellular material. This structure withstands high hydrostatic pressures for long periods of time without serious loss of effectiveness as an underwater reflector. Compartmentation of the cellular core material avoids flooding the entire sheet in case of a puncture or failure. The size of each compartment depends on the application.

In operation the acoustic panel is directly exposed to the water or other fluid in which sound reflection is desired. Sound reflection is provided by the compliant cellular material. The gas-impermeable material prevents the diffusion of the gas from the cellular material. The outer protection layer is for protection against mechanical damage and fluid seepage which might have injurious elfect on the gas-impermeable envelope.

There are several alternate methods of construction in addition to the particular embodiment described. In each case the center core would be a number of pieces of cellular rubber or compliant cellular plastic. A coating of a compliant material which is impermeable to the gas contained in the cells of the cellular material would be applied to the cellular material by either wrapping and sealing or by dipping, painting, or casting. Another protective layer is then applied for mechanical protection and waterproofing. The gas-impermeable coating may also serve as a protective layer it the right material is used.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

, 1. A compartmentedacoustic panel which is adapted for intimate wrapping thereof around bodies of complicated, uneven configurations comprising a base comprising a sheet of flexible rubber, a plurality of substantially parallel acoustic reflectors spaced from one another on and secured to a face of said base, each of said reflectors comprising a thin sheet of cellular elastic material and a thin, fluid impervious envelope entirely encasing said cellular sheet and sealed fluid tight, and a covering sheet of rubber substantially equal in area to said rubber base over the exposed surfaces of said reflectors and the re maining portions of said rubber base sheet, said rubber Patented Apr. I 28, 19 5?.

base sheet and said blanketing sheet being in intimate coincident contact to provide a water-tight seal.

2. An acoustic panel as defined in claim 1 wherein said elastic material is cellular rubber. 3. An acoustic panel as defined in claim 1 wherein said elastic material is a cellular plastic.

' 4. A compartmented acoustic reflector panel which comprises a sheet of flexible elastic material, a plurality of plate-like acoustic reflectors secured flat against a face of said sheet in sidewise spaced apart relationship, each reflector being formed of a thin sheet of cellular elastic material encased in a fluid tight envelope of impervious, thin, freely flexible material, and strips of elastic material fitted in the spaces between said reflectors and secured to said first mentioned sheet.

5. The panel as set forth in claim 4, wherein the cellular elastic material is cellular rubber.

References Cited in the file of this patent UNITED STATES PATENTS Merritt May 17, 1921 Wood et a1. Apr. 6, 1937 Turner Oct. 26, 1943 Black Nov. 12, 1946 Goodale Nov. 26, 1946 Beechlyn Apr. 5, 1949 Mell et al Jan. 31, 1950 Lewis Nov. 11, 1952 FOREIGN PATENTS Great Britain Feb. 28, 1922 

